1. Field of the Invention
The present invention relates to a control rod/fuel support grapple and, more particularly, a control rod/fuel support grapple which is capable of picking up simultaneously control rods and a fuel support in a boiling water reactor (referred to as a xe2x80x9cBWRxe2x80x9d hereinafter).
2. Description of the Related Art
FIG. 8 is a vertical sectional view showing a part of the core of the BWR. As shown in FIG. 8, a cylindrical core shroud 2 is provided in an inside of a reactor pressure vessel 1 and a plurality of fuel assemblies 3 are loaded in the core shroud 2. A plurality of control rods 4 each having a cruciform lateral sectional shape are arranged vertically movable in clearances between the fuel assemblies 3. Each of the control rods 4 has a hoist handle 4d at its top end. Core reactivity can be controlled by moving up and down these control rods 4 in the core.
A top end of the fuel assembly 3 is supported by an upper grid 5. A bottom end of the fuel assembly 3 is supported by a core support plate 7 via a fuel support 6. FIG. 9 is a perspective view showing a part of the upper grid 5 of the BWR. As shown in FIG. 9, a plurality of grids into which the top ends of a plurality of fuel assemblies 3 are inserted respectively are formed on the upper grid 5.
As shown in FIG. 10, a plurality of fuel support sustaining holes 7a are formed in the core support plate 7, and the fuel supports 6 can be supported by the core support plate 7 by inserting their cylindrical bottom portions into the sustaining holes 7a respectively. As shown in FIG. 11, for example, sustaining holes 6a, 6b, 6c, 6d and a cruciform shaped through hole 4a are formed on a substantially square cylinder type upper surface portion of the fuel support 6. Then, bottom portions of four fuel assemblies 3 can be inserted into the sustaining holes 6a, 6b, 6c, 6d respectively and then supported thereon. The cruciform control rod 4 can be moved vertically through the cruciform through hole 4a. 
The sustaining holes 6a, 6b, 6c, 6d of the fuel support 6 are connected to orifices 6e, 6f, 6g, 6h formed on a side peripheral wall of the fuel support 6 respectively such that coolant is supplied from the orifices 6e, 6f, 6g, 6h to the fuel assemblies 3 via the sustaining holes 6a, 6b, 6c, 6d respectively. In addition, a slot 6i into which a fixing pin 7b (provided on the core support plate 7) is inserted is formed on an upper corner portion of the fuel support 6. The fuel support 6 can be fixed to the core support plate 7 via the slot 6i. 
Also, as shown in FIG. 8, a plurality of control rod drive mechanisms (CRDs) 8 are provided so as to pass through a bottom portion of the reactor pressure vessel 1 vertically. The control rods 4 are detachably attached to the control rod drive mechanisms 8 respectively. Top ends of a plurality of control rod guide tubes 9 are coupled to the core support plate 7. The fuel supports 6 are arranged on the top ends of the control rod guide tubes 9 respectively. The control rod 4 can be driven vertically by the control rod drive mechanism 8 such that the control rod 4 can be inserted into or withdrawn from the core through the inside of the control rod guide tube 9 and the cruciform through hole 4a of the fuel support 6.
As shown in FIG. 12, the control rod 4 and the control rod drive mechanism 8 are coupled with each other by a spud coupling type coupling mechanism. More particularly, they are coupled via a spud coupling 10. A coupling spud 11 whose periphery is divided by cuttings to form quartered latching pawls, for example, is pushed upward by a drive piston (not shown) of the control rod drive mechanism 8. The coupling spud 11 can be tightly pushed into a clearance formed on the out side of a periphery of a lock plug 12 which is inserted into the fitting holes of a lower end 4b of the control rod 4. As a result, the coupling spud 11 is supported by both an inner peripheral surface of the lower end 4b of the control rod 4 and an outer peripheral surface of the lock plug 12, so that the control rod 4 and the control rod drive mechanism 8 can be coupled with each other.
There are two methods of uncoupling the control rod 4 and the control rod drive mechanism 8, i.e., one is such a method that can be applied from a pedestal side of the bottom portion of the reactor and the other is such a method that can be applied from an upper side of the reactor. In the event that the releasing operation is applied from the pedestal side of the bottom portion of the reactor, as shown in FIG. 12, the lock plug 12 is pushed upward by an uncoupling rod 13 of the control rod drive mechanism 8 against a spring force of a spring 4c, whereby a coupled state of the control rod 4 and the control rod drive mechanism 8 are uncoupled.
In turn, in the event that a releasing operation is applied from the upper side of the reactor, at first the fuel assembly 3 is pulled up from the core. Then, the fuel support 6 can be pulled up from the core by means of a manipulating tool which can manipulate the fuel support 6. Then, the manipulating tool can be replaced with a dedicated control rod latch tool which can hold the control rod 4 and then release the control rod 4 and the control rod drive mechanism 8. They can be released by operating a release handle 20 (latching handle) 4e (see FIG. 8) of the control rod 4 by use of this control rod latch tool, and thereafter the control rods 4 can be pulled up from the core.
At any rate, during a periodical inspection of the BWR, both reduction in working time and reduction in operator""s exposure are desired. An exchange operation of the control rods 4 is not an exception.
In the related art, in order to reduce a time required for the exchange operation of the control rods, at first an uncoupling operation (coupling releasing operation) of the control rod and the control rod drive mechanism is carried out from the pedestal side of the bottom portion of the reactor by using the control rod drive mechanism, and then the control rods and the fuel support are picked up simultaneously from the core from the upper side of the reactor by using the conventional control rod/fuel support grapple, whereby the exchange operation of the control rods is performed.
However, as described above, in the exchange operation of the control rods by use of the control rod/fuel support grapple method in the related art, since at first the uncoupling operation of the control rod and the control rod drive mechanism has been carried out from the pedestal side of the lower portion of the reactor by using the control rod drive mechanism and then the control rods and the fuel support have been picked up from the core simultaneously from the upper side of the reactor by using the conventional control rod/fuel support grapple, two stage operations have been required which causes a longer working term.
In addition, in the event that the uncoupling operation of the control rod and the control rod drive mechanism is applied from the pedestal side of the bottom portion of the reactor, there has been a problem of the operator""s exposure in the related art. For this reason, it has been requested that the operator""s exposure would be reduced by executing the exchange operation of the control rods without the operation conducted at the bottom portion of the reactor.
Therefore, it is an object of the present invention to provide a control rod/fuel support grapple (abbreviated as a xe2x80x9cCR/FS grapplexe2x80x9d hereinafter) which is capable of pulling up simultaneously control rods and a fuel support and also carrying out an uncoupling operation of the control rod and a control rod drive mechanism.
In order to achieve the above object, according to the present invention, there is provided a control rod/fuel support grapple comprising a control rod holding means for holding a hoist handle provided to a top end of a control rod, a fuel support holding means for holding a fuel support which supports a bottom end of a fuel assembly, a coupling releasing means for releasing a coupled state between the control rod and a control rod drive mechanism by virtue of spud coupling, and a main body frame to which the control rod holding means, the fuel support holding means, and the coupling releasing means are attached and which can be hung down into an inside of a reactor pressure vessel.
Preferably, the coupling releasing means includes a coupling releasing link mechanism for operating a control rod""s release handle, and a coupling releasing cylinder for driving the coupling releasing link mechanism.
Still preferably, the control rod holding means can be displaced relative to the main body frame along a longitudinal direction of the control rod by a predetermined width.
Still preferably, the control rod/fuel support grapple further comprises an operational timing control mechanism for releasing a coupled state between the control rod and the control rod drive mechanism by using the coupling releasing means after the hoist handle being held by the control rod holding means.
Still preferably, the control rod holding means includes a pivotable hook adapted to be hooked onto the hoist handle, and a control rod holding cylinder for carrying out a pivot operation of the pivotable hook.
Still preferably, the coupling releasing means includes a coupling releasing link mechanism for operating a control rod""s release handle, and a coupling releasing cylinder for driving the coupling releasing link mechanism, the control rod holding cylinder and the coupling releasing cylinder are driven by a common working fluid source, and the operational timing control mechanism is such a mechanism that can reduce an operation speed of the coupling releasing cylinder to be smaller than an operation speed of the control rod holding cylinder.
Still preferably, the operational timing control mechanism is composed of a damper mechanism for applying resistance to a piston rod of the coupling releasing cylinder in its operation.
Still preferably, the operational timing control mechanism is composed of a flow restrict mechanism which is provided in a middle of an working fluid pipe connected to the coupling releasing cylinder.
Still preferably, the hook is formed of a hook-shaped member, and a self-weight of the control rod operates to hold a hooked state of the hoist handle by the hook after the control rod has been lifted up via the hook.
Still preferably, the fuel support holding means includes a fuel support holding link mechanism for holding a top end of an orifice of the fuel support, and a fuel support holding cylinder for driving the fuel support holding link mechanism.
Still preferably, the fuel support holding link mechanism has contact a back-and-forth movable piece adapted to be connected to the top end of the orifice, and a stepped portion on which the upper portion of the orifice is placed being formed on the contact piece such that back and forth motions of the contact piece can be inhibited in a state that the upper portion of the orifice is placed on the stepped portion.
Still preferably, the control rod/fuel support grapple further comprises a detecting means for checking a holding state of the control rod holding means, a holding state of the fuel support holding means, and a releasing state of the coupling releasing means respectively.
Still preferably, the control rod holding means and the coupling releasing means are detachably attached to the main body frame, the fuel support holding means and both the control rod holding means and the coupling releasing means can be employed independently respectively as separate bodies by detaching the control rod holding means and the coupling releasing means from the main body frame.